The present invention relates to ion beam sources, particularly to an additional exit or collimating grid for an ion source, and more particularly to an addition grid which collimates ion beamlets and disallows beam spread and limits the beam divergence during transients and steady state operation.
The ion beam source used in an ion beam sputter deposition (ISBD) tool typically is focused and neutralized to ensure that the ion beam hits the center of the sputtering target during operation. The target is made large so that all the beam is intercepted. In practice, the ion beam during turn-on and turn-off becomes defocused and the ions hit the outer periphery of the target and may miss the target completely. During the coating cycle of substrates, particularly involving multilayer coatings, there is re-deposited material on the periphery of the target and deposited materials on the walls of the deposition chamber. Ions that hit the re-deposited material and/or hit the material deposited on the vessel walls may dislodge particulates which can become defects on the substrate being coating. Thus, there is a need for preventing defects on the substrate from either the re-deposited target material or the material deposited on the walls of the deposit ion chamber. Defects on substrates, such as used for masks in lithographic applications, produce a major problem.
The present invention provides a solution to the above defect problem by providing the ion source with an additional exit or collimating grid that ensures that the ion beam will hit and be confined to a specific target area, thereby collimating the ion beamlets and disallowing beam spread during turn-on and turn-off of the ion beam. Thus, the collimating grid prevents ions from hitting the peripheral re-deposited target material and/or from hitting material deposited on the walls of the deposition chamber.
It is an object of the present invention to provide an improved ion beam source.
A further object of the invention is to provide an ion beam collimating grid to reduce deposition defects.
A further object of the invention is to provide an ion source with means which disallows beam spread and limits the beam divergence during turn-on and turn-off.
Another object of the invention is to add to the ion source grid set an extra exit grid.
Another object of the invention is to provide an ion beam source with an additional exit grid which collimates the ion beamlets, and disallows beam spread, and limits the beam divergence during transients and steady state operation.
Another object of the invention is to provide an ion beam source with a collimating exit grid which prevents the ion beam from hitting the periphery of the target or hitting material deposited on the walls of a deposit chamber.
Another object of the invention is to provide an ion source for deposition applications where minimization of defects on the substrate being coated is critical, such for defect free masks for extreme ultraviolet lithography (EUVL).
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. Basically, the invention involves the addition of an extra exit or collimating grid to an ion source grid set. Thus, in addition to the typical ion source grid set comprising an entrance grid, a suppressor grid, an exit grid, the present invention adds a collimating grid spaced downstream beamwise from the exit grid. The collimating or added exit grid collimates the ion beamlets, disallows beam spread, and limits beam divergence. Thus, during turn-on, turn-off, or other transient, as well as steady operations, the added grid prevents ions of the ion beam from hitting the periphery of the target or missing the target and hitting the wall of the deposition chamber. Thus, particles, resulting in defects on the substrate being coated, which are caused by ions hitting re-deposited material on the periphery of the target or deposited material on the walls of its deposition chamber are eliminated. Thus, by the use of the collimating grid, defect free masks, for example, as required for EUVL systems, or other applications where minimization of particulates on the substrate being coated is important, can be produced.